DESCRIPTION Addiction to drugs of abuse such as cocaine and ethanol is a major problem facing our society. Although basic research efforts have made great strides in understanding how drugs of abuse can usurp the function of the mesolimbic "reward pathway" of the brain, our knowledge of these mechanisms at the cellular level is far from complete. Research indicates that the serotonergic system plays a role in the mechanisms of drugs of abuse, especially cocaine and ethanol. At present, however, our knowledge of the effects of serotonin in key areas of the mesolimbic reward pathway, such as the nucleus accumbens (NAc), is lacking. The goal of the research outlined in this proposal is to elucidate the actions of serotonin (5-hydroxytryptamine; 5-HT) on excitatory and inhibitory synaptic transmission in the NAc using whole cell recording techniques in an in vitro brain slice preparation. These experiments will provide fundamental information about the role of serotonergic systems in the function of the NAc-information that is a prerequisite to understanding how the system may be altered by exposure to drugs of abuse.